The present invention relates to motor vehicles. More particularly, the invention relates to on-highway vehicles designed to operate at highway speeds.
Special terms used herein are defined as follows:
Forward: Toward the front end of the vehicle.
Aft: Toward the rear end of the vehicle.
Highway speeds: Speeds in excess of fifty miles per hour.
Extended motor vehicle: A motor vehicle having an elongated, integral chassis.
Elongated: Substantially longer than a conventional automobile or "pickup" truck; having a length of from about twenty feet to about forty feet.
Integral: Unitary; not segmented; not formed e.g. like a tractor-trailer.
Axle: A shaft which connects wheels located on opposite sides of a frame which is supported by the shaft.
Short axle: A shaft which connects a pair of wheels on the same side of the frame.
Spindle: A short conical shaft on which a wheel is mounted.
Driving axle: Axle that is power-driven.
Fixed axle: An axle permanently aligned in a particular configuration with respect to the frame.
Steerable axle: An axle which is capable of changing direction with respect to the frame.
Tandem axles: A pair of axles very near one another; not spaced apart or separated by a distance of more than about two or three feet.
Tridem axles: Three axles very near one another; not spaced apart or separated by a distance of more than about two or three feet.
Spread axles: Axles spaced apart and separated by a distance of from about four feet to about six feet.
Fixed wheel: A wheel the orientation of which remains unchanged with respect to an axle on which the wheel is mounted.
Steerable wheel: A wheel which is capable of changing direction with respect to and independently of a fixed axle to which the wheel is connected by a spindle.
Microprocessor: Any electrical device or combination of electrical components which is capable of performing the functions of a microprocessor as set forth in the specification and claims.
Much of the background information relating to the present invention may be found in U.S. Pat. No. 4,740,006 to Ducote and in application Ser. No. 377,292, which are hereby incorporated by reference.
Motor vehicles encompassed by the present invention include tractor-trailer assemblies, recreational-vehicle (RV) motor homes, boat-trailer assemblies, trucks, busses, moving vans, and passenger vans.
Trucks, tractors, and trailers are well described in the Encyclopedia Britannica, volume 18, pages 721-723, hereby incorporated by reference.
More specifically, reference is made to FIGS. 1 and 2, which represent prior-art embodiments of extended motor vehicles.
A first prior-art embodiment 2 (FIG. 1) comprises a frame 9 and chassis 10 mounted on a first fixed axle 4 with steerable wheels 3 connected thereto. This first axle 4 is positioned at or near the front end of the vehicle 2. A pair of tandem axles 4 support the rear end of the vehicle. The tandem axles 4 are provided with fixed wheels 3a.
A second prior-art embodiment 7 is shown in FIG. 2. In this embodiment the frame 9 and chassis 10 are mounted on a first fixed axle 4 having steerable wheels 3 at or near the front end of the vehicle 7, and a group of tridem fixed axles with fixed wheels 3a at or near the rear end of the vehicle 7.
Special and serious problems are inherent in the vehicles depicted in FIGS. 1 and 2, because of the tandem and tridem axles 4 and the fixed wheels 3a. Each axle 4 of the tandem and tridem arrangement, when the vehicle 2 or 7 is making a turn, is continuously dragging and destabilizing the wheels 3a of the lead axle 4. This can cause loss of control to a greater or lesser extent, depending upon the speed of the vehicle and the sharpness of the turn. Other undesirable effects include excess tire wear and loss of the extra energy required to overcome the sliding friction of the rear wheels, as compared to rolling friction. Moreover, the sidewise dragging of the wheels 3a and axles 4 causes excessive wear of the axles, suspensions, and other components, thereby increasing maintenance and replacement costs. Fire trucks and other extended emergency vehicles are at risk with respect to loss of stability, particularly at high speeds and in congested traffic. All of these potential and inherent problems apply to mobile homes and extended military vehicles, as well as to tractor-trailer combinations.
A second problem inherent in the prior-art extended vehicles is a long wheel base or turning radius. Because the only steerable wheels are in the front end of the vehicle, all of the strain of steering the vehicle in a turn falls thereon, with the frequent result that the front wheels fail to "grab." They slip, thereby causing the vehicle to make an excessively wide turn. In so doing, the vehicle often "rides" on the curb or swings into the lane of oncoming traffic. Both situations are rife with hazard.
U.S. Pat. No. 1,402,175 to Overman, issued Jan. 3, 1922, discloses municipal and cross-country trucks having more driving wheels than two, in order to increase the traction and pulling power of such motor vehicles, and to distribute the load over more points of support. Overman discloses a truck chassis having eight wheels, six of which are drivers. Steering knuckles (9,9) are pivoted to the front axle, and are connected by a parallel rod (10). Wheels (11,11) are mounted on the steering knuckles (9,9). A block (7) rests upon a fifth wheel which is connected by a king pin (13) with a longitudinal bolster (14). Each end of the bolster (14) bears upon the fifth wheel and are respectively connected by king pins (15 and 16) with transverse bolsters (17, 18). The bolsters (17,18) have eyes to which diagonal rods (36,37) are connected by pivot bolts through corresponding eyes in the ends of the rods, so that when bolster 17 is moved about king pin 15, bolster 18 is moved correspondingly in an opposite direction. The front bolster 19 is connected with the main frame (5) by diagonal rods (38,39). When the front wheels are manually turned by moving the steering knuckles (FIG. 1) or the front axle (FIG. 4), the front end of the body 5 correspondingly follows their lead, and the body turns about king pin 13 as a center, whereupon the diagonal rod 38 (FIG. 4) swings the front bolster (17) about king pin 15, and the rod 37 swings the rear bolster 18 about king pin 16, to cause the vehicle to make a curve properly without interfering with the power transmission from the motor to the axles through the propeller shafts and gears. A middle bolster (21) is rigidly connected to the longitudinal bolster 14 and is thereby controlled in its position by the bolster 14. There are thus no fixed axles in the motor vehicle disclosed by Overman, and steerage is by steerable axles.
U.S. Pat. No. 1,454,162 to Furlong, issued May 8, 1923, discloses motor vehicle having a first fixed axle at the front end, with steerable wheels mounted thereon and steered by a steering wheel. There is a first steerable axle at the rear end of the vehicle. There is a second fixed axle with fixed wheels just aft of the first fixed axle; and a second steerable axle forward of the first steerable axle and aft of the second fixed axle. There is no second fixed axle with steerable wheels.
U.S. Pat. No. 1,835,112 to Hawkins, issued Dec. 8, 1931, discloses a motor vehicle having at least three pairs of proximately-located wheels, in which the load distribution to the wheels is such that a simple light steering mechanism can be employed and in which the load is distributed equally or as desired to each of the wheels. Each of the driving axles (326) are spaced from the main frame (327) by torque arms (328) rigidly affixed to the axles and universally connected to cross members (329). Each driving axle (326) is provided, adjacent one end, with a hemispherical saddle (331) in which a ball (332) is seated and retained for universal movement by an apertured hemispherical cap (333). An upright stem (334) is attached to the ball (332), and extends through the aperture in the cap (333). The stem is enlarged intermediate its ends to form a piston (336) which is free to slide in a cylinder (337) depending from a housing (338) affixed to the main frame (327) by a ball-and-socket joint (339). The upper end of the stem (334) is enlarged into a mushroom or circular convex disc 341 which bears against a bag (342) of rubber or other suitable material retained in the housing (338) by an apertured cap (343). The bag (342) is connected by an elbow (345) and a flexible hose (344) to a pipe (346) which serves as a main interconnection of the hoses of all the pneumatic cylinders disposed along one side of the vehicle. One side of each driving axle (326) is provided with a cylinder (347) mounted between two ball-and-socket joints as described, while the other side of the axle is provided with a similar cylinder (347) connected to the axle by a ball-and-socket joint (348) and to the main frame (327) by a pin (349) journalled in a bracket (351) attached to the frame. The non-driving axles (352) are also provided with pneumatic cylinders (347) adjacent each end. The cylinders (347) are rigidly attached to the main frame (327), and one of them is pivoted to the axle (352) by a pin (353) which passes through a forked seat (354) on the axle, and through an aligned aperture in the rod (356) which is otherwise similar to the rod 334. The other pneumatic cylinder is attached to the axle 352 by a shackle comprising a link (357) pivoted at one end to a forked seat (358) on the axle, and pivoted at the opposite end to the rod (359) in other respects like the rod (334). From the foregoing description it should be clear that it is the axles, not the wheels, which are steered. In a second embodiment steerable wheels are mounted directly on the frame.
U.S. Pat. No. 1,856,787 to Schellentrager et al., issued May 3, 1932, discloses a motor vehicle comprising a frame, a load-carrying platform mounted on the frame, drive and steering wheels carried by the frame, a steering mechanism for the steering wheels, a source of power supported on the frame, power means to propel and to load the vehicle, control means for the vehicle, and safety means for the vehicle. The frame is articulate, and comprises parts A, B, C, D, and E hinged together. Hence, the vehicle disclosed by Schellentrager et al. is neither a unitary extended vehicle nor a tractor-trailer assembly.
U.S. Pat. No. 1,871,432 to Fageol, issued Aug. 9, 1932, discloses a road vehicle having two pairs of steerable wheels mounted on two fixed axles at the front end of the vehicle. These axles and wheels are in tandem. There are two fixed axles bearing fixed wheels at the rear of the vehicle, also in tandem. There are no spread axles. There are no steerable wheels aft of the front wheels.
U.S. Pat. No. 3,486,576 to Breon et al., issued Dec. 30, 1969, discloses a steering system for a multiple-axle vehicle. The steering system includes a plurality of hydro-mechanical steering-jack systems interconnected by a mechanical linkage which has an anticipator cylinder therein for taking up slack in the linkage regardless of the direction in which the vehicle is to be steered. Steerable wheels are mounted directly on the frame, not on axles.
U.S. Pat. No. 4,740,006 to Ducote discloses a remote-control steering system for tractor-trailer assemblies and the like. All trailer axles are load-bearing and fixed. The rearmost axle on the trailer has fixed wheel mountings, and serves as a pivot for turning the trailer when it moves in either a forward or a reverse direction. The axle or axles located forward of the rearmost axle of the trailer and aft of the trailer king pin has or have directional wheels that automatically track and follow in concentric pattern the path of the rear wheels of the towing vehicle. The motive force for steering the directional wheels emanates from a sensor nested in the V-slot of the fifth wheel of the towing vehicle. The steering system is designed to be installed as a retrofit to existing trailers, or as optional equipment for trailers not yet manufactured. Abling and disabling the system is automatic. Abling takes place when the fifth wheel is moved into position to couple the king pin of the trailer. The system is disabled when locking lugs for the fifth wheel are released, and the fifth wheel moves away from the king pin.
British (GB) Patent No. 148,255 discloses a motor vehicle which includes an airscrew-drive in combination with means enabling the vehicle to travel on difficult terrain. The enabling means comprise three or more axles and a corresponding number of wide wheels. There are from two to four fixed axles with steerable wheels, but there is no fixed axle with fixed wheels to act as a pivot point.
GB Patent No. 525,824 discloses a motor vehicle having one pair of driving wheels each with twin tires thereon, the driving axle being loaded to carry approximately twice the load applied to any of the other three pairs of wheels, each of which has a single tire thereon. There are two pairs of wheels which are moved for steering purposes. The other pair of non-driven wheels may be disposed either in front or to the rear of the driven wheels. There is one pair of steerable wheels on a first fixed axle at the front end of the vehicle. There is a second pair of steerable wheels on a second fixed axle aft of the first axle. There are two pairs of fixed wheels on a third fixed axle aft of the second axle. There is one pair of fixed wheels on a fourth fixed axle at the rear end of the vehicle or forward of the third axle. The two forward axles are spread; the two aft axles are tandem. There are no steerable wheels at the rear end of the vehicle.
Tractor-trailer combinations known as "eighteen-wheelers" present special problems. FIG. 12 shows a top plan view of a first type of eighteen-wheeler presently in use, generally denoted by the numeral 9a. The frame 10a of a trailer 2a is supported near the front end by the frame 7a of a tractor 1a. The frame 7a is supported by a fixed front axle 4 provided with a pair of steerable wheels 3 mounted on a pair of spindles 6, and by two fixed rear axles 4, each of which is provided with two pairs of fixed wheels 3a. The trailer frame 10a is further supported by two fixed axles 4 near the rear of the trailer 2a. Each of these rear axles 4 is likewise provided with two pairs of fixed wheels 3a. A "fifth wheel" 8a is fastened to the frame 7a of the tractor 1a.
There are serious disadvantages inherent in the eighteen-wheeler 9a. The following examples are illustrative of the problems inherent therein.
(1) Because the only axles supporting the frame 10a of the trailer 2a are the two rear axles 4, approximately half the weight of the trailer 2a is borne by the frame 7a of the tractor 1a. An immediate consequence of this burden on the tractor 1a is that tractors pulling eighteen-wheelers must be large, heavy, and rugged enough to bear about half the weight of the trailer and of the payload, as well as the weight of the tractor itself. Clearly, if part of this extra weight could be borne by the trailer, it would be possible to utilize lighter and less expensive tractors. Furthermore, the portion of the fuel utilized to move the tractor alone could be considerably reduced, leading to even greater savings and to a significant advantage in fuel economy and energy conservation.
(2) Because there are only fixed wheels 3a supporting the trailer 2a, it is impossible for the trailer 2a to turn without some of the wheels 3a skidding or dragging to some extent. The farther apart the rear axles 4, the more serious is the problem of wheel drag. This problem causes loss of control, wasteful loss of rubber from the tires mounted on the wheels 3a, and wasteful loss of the extra energy required to overcome sliding friction as opposed to rolling friction. The trailer 2a is unstable in a turn. The faster the speed and the sharper the turn, the greater the instability.
(3) The fifth wheel 8a of the tractor 1a furnishes a leg to support the front end of the trailer 2a. However, it does not furnish full support for the full width of the front end of the trailer 2a. This deficiency causes the bed (not shown) of the trailer 2a to rock down on one side and up on the other side. The extent to which such rocking occurs depends on the turns that the trailer 2a makes, the imbalance of the load (which can be caused by shifting of the cargo in transit), road conditions, and other variables. This particular type of instability is almost continuous while the eighteen-wheeler 9a is in motion.
(4) Often the longitudinal center of the trailer, when loaded, is in continual up-and-down motion. This motion contributes to the instability of the trailer 2a, and may in extreme cases cause the trailer 2a to collapse at the longitudinal center.
(5) The looseness of the trailer king pin (not shown) in the fifth wheel 8a of the tractor 1a causes some shock, which contributes to a deficiency in traction and to a rough ride for both cargo and driver.
(6) Tandem axles are not equivalent to two single axles. Transportation authorities do not allow as much weight to be carried by a pair of tandem axles as by a pair of single axles.
(7) Tandem axles on either the tractor 1a or the trailer 2a, because they drag in a turn, can individually or in combination initiate a slide of the eighteen-wheeler 9a into a "jack-knife."
(8) The trailer 2a cannot independently furnish braking for the trailer and its payload (not shown). The push of the trailer 2a against the tractor 1a when brakes are applied to the tractor 1a causes the tractor 1a to yaw.
(9) There is nothing between the trailer 2a king pin (not shown) and the rear axles 4 of the eighteen-wheeler 9a to function as a load-bearing stabilizer for the trailer 2a. It is part of the function of the massive tractor 1a to counteract the sideward pull of the trailer 2a upon the tractor 1a when the tractor changes direction at highway speeds. The sharper the turn and the greater the speed, the greater is the pull of the trailer 2a on the tractor 1a.
(10) The existence of the problems just enumerated has caused the gradual emergency of heavier and more massive tractors 1a. These massive tractors have larger engines. The role of the tractor 1a is to pull, to steer, and to give stable traction to the eighteen-wheeler 9a while carrying its cargo at highway speeds. The heavier tractors 1a, along with Transportation Department load limits on tandem axles 4, cause the eighteen-wheeler 9a to carry less of a payload. The increased horsepower of the tractor 1a engines (not shown) results in lower fuel efficiency. These factors, in combination, raise the cost per ton-mile of hauling freight substantially.
In an attempt to alleviate these problems, prior-art devices have utilized steerable axles with fixed wheels for eighteen-wheelers; see, for example, U.S. Pat. Nos. 3,149,858, 3,533,644, 3,712,641, 3,734,538, 4,120,509, 4,244,596, and 4,463,966.
Special devices have also been devised for steering goose-neck trailers, the devices including steerable short axles, wheels steered by friction against the road, and rear wheels forcibly steered from the fifth wheel of the tractor.
These prior-art devices are expensive to manufacture and maintain; and, because of their specialized design, of limited utility. Additionally, the devices and methods described in these patents are not effective for negotiating high-speed turns on highways and public streets. They are, moreover, difficult to connect and disconnect. More specifically, when steerable axles are used to make a turn, the base of support provided by the axle is diminished proportionately to the degree of the turn.
More recently, a significant advance in the technology was made by Ducote, as disclosed by U.S. Pat. No. 4,740,006. Ducote discloses a steering system for use in a tractor-trailer combination in which all trailer axles are load-bearing and fixed. The rearmost axle on the trailer has fixed wheel mountings, and serves as a pivot axle for turning the trailer when the trailer moves in either forward or reverse direction. The axle or axles located forward of the rearmost axle of the trailer and aft of the trailer king pin has or have directional wheels which automatically track and follow in concentric pattern the path of the rear wheels of the tractor. The force for steering the directional wheels emanates from a sensor nested in the V-slot of the fifth wheel of the tractor. The system is capable of being retrofitted to existing trailers, or optionally being used as equipment for trailers not yet manufactured.
While Ducote's invention represents a tremendous advance over existing technology for solving the problems enumerated above, there have since come into prominence trailers with spread-tandem axles. As stated above, the greater the spread of the tandem axles, the more serious the problem of wheel-drag becomes. Spread-tandem axles are conventionally separated by a distance of about ten feet. Such a trailer is shown in FIG. 13 and designated by the numeral 2b.
These rigid spread-tandem axles with fixed wheels add another dimension to turning, in that these spread axles must be dragged around to make the turn. The distance by which the tires and wheels are dragged depends on the individual axle loads and the road surface under each of the tires. In any case they must be dragged into alignment, for every turn that the rig makes. To compensate for this sideways dragging, the driver makes an extra-wide turn. So, in the first place the driver turns wide to accommodate the length of the trailer; and in the second place, the driver turns wider yet to have additional distance for the dragging and instability of the rigid tandems to turns. The reason that the rigid spread tandems are used is that they are allowed the axle weight of single axles. This allowable weight is 20,000 pounds per axle. This helps them get through the Department of Transportation weight scales. This severe problem is evident at the access and exit ramps of interstate highways.
These problems are always with the driver. When driving in cities, the driver must find an intersection at which the driver is able to make a turn. The turn that is made is seldom an easy turn; it is a turn that the driver is barely able to make. Thus the driver and the rig must roll until the driver is able to find a suitable intersection. The time spent finding this begins at the point that the vehicle is loaded, and ends at the point the load is discharged.
"Sliders" are rear-axle groups mounted as a truck which is slidable on the beams of the trailer. One function of the slider is to shorten the wheelbase when the rig is unable to back into a tight place for unloading. When the driver sees that he or she is unable to back into an unloading spot, the driver parks the rig, gets out of the cab, manually unlocks the slider, gets back into the cab, locks the wheels of the slider, then backs up a few feet to shorten the wheelbase. The driver parks the rig again, and gets out of the cab again, and locks the slider again in this new position under the trailer. He or she gets back into the cab a third time, and backs the rig to a spot where it can be unloaded. Though the driver has shortened the wheelbase, it is still usually not short enough. The driver will still run over curbs and medians, in order to get the rear of the trailer to the right spot.
"Extendables" are semi-trailers that telescope out to accommodate the length of reinforced concrete pilings, steel beams, and other structural members. These extended trailer have aggravated problems in turning because of their extra length.
Military semis are used to transport tanks and other military vehicles and equipment. These long semi-trailers have all of the problems of other long semi-trailers. Additionally, they are used in peaceful transport of military vehicles in old-world cities. The streets in many of these old-world cities are narrow, having been built for horse-drawn vehicles. Due to the present international situation, an extraordinary number of military semis are in use.
Transportation needs have caused semis to be built longer as time goes on. The longer the semi-trailer, the more difficult it is for the tractor-trailer 9a (FIG. 13) to get around an intersection or make a turn. There are many instances every day of tractor-trailers intruding in the adjacent lanes of traffic to make a turn. This is a dangerous practice, and disrupts traffic that is sometimes already heavy. Another problem is that the rear wheels of the trailer 2b ride over the curbs, sidewalks, and medians. This demolishes curbs and street signs, and brushes utility poles, which is damaging to both the trailer and the utility pole. This problem is particularly severe at intersections and ramps that lead to and from interstate highways.
Emergency vehicles and hook-and-ladder semis for fire-fighting have a greater problem with this situation because of the length of the semi-trailers.
To alleviate the problems arising from spread axles, dump valves are being used for one of the two axles on the spread. By exhausting the air springs of one axle, the axle no longer is under load and can travel through a tight curve more easily. Most spread-tandem platforms dump the air from the rearmost axle. By doing so, the platform has the maneuverability of a trailer that is significantly shorter.
Suspension manufacturers teach that the dump-valve system was intended for limited use, such as tight ninety-degree turns, backing into loading docks, maneuvering within a yard, and other "creep-speed" applications. But the improved maneuverability is leading some drivers to dump air when making moderate curves at speeds of about thirty miles per hour.
Accordingly, some trailer and component manufacturers are starting to object to what they consider abuse of the dump valve. The Spicer Trailer Products Division of Dana Corporation issued an engineering update stating that the company would not warrant the axles used on spread-axle trailers equipped with dump valves. In pertinent part, the update reads as follows:
"When a dump valve is actuated, the axle equipped with the dump system sees only its own weight and that of the attached suspension components, unless a regulator is used to maintain some air pressure in the air bag. The other axle sees the full load normally carried by both axles, causing severe overloading of that axle. Unless such dump valves can be provided to automatically apply air pressure above speeds of five mph, Spicer Trailer Products does not approve, and will not warrant axles used on spread axle trailers equipped with dump valves."
Great Dane does not offer dump valves on spread-axle platforms for increasing maneuverability or reducing tire-scuffing. "We will put dump valves on both axles in order to control dock height, but we won't put them on just one axle," states Paul Crabtree, manager of engineering at Great Dane's platform plant in Memphis, Tenn. "We will put them on lift axles if a tandem is already in place, because we are assuming that the trailer will be operated with the axle lifted. The trailer will have to be built to handle that."
Clearly, these attempts by the prior art to solve problems associated with spread-tandem axles on eighteen-wheelers fall far short of providing satisfactory solutions to these problems.
A basic cause of both these problems is the use of axles with fixed wheels. Whether the axle is a fixed axle or a steerable axle, the axle is not adaptable to being steered without a significant amount of drag.